1. Field of the Invention
The present invention relates to a method and an apparatus for soldering for a work conveyed to a predetermined working position by using soldering irons. Further, the present invention relates to a soldering land of a printed circuit board having a slit which is formed for inserting a metal plate.
2. Description of the Related Art
In a conventional soldering method, a soldering iron is disposed above a manufacturing line by which printed circuit boards are successively conveyed. On the printed circuit board, circuit components are mounted. The soldering iron descends toward the printed circuit board conveyed to a predetermined working position and soldering is automatically performed, supplying solder to a tip of the heated soldering iron. In this method, if oxidized solder gathers around the iron tip, soldering performance is greatly lowered. Therefore, an air blow is carried out to clean the iron tip once in five to twenty times of the soldering.
As to the above method, working of the soldering is interrupted while cleaning is carried cut. Thus, operating efficiency of equipment is low. Further, upon carrying out the cleaning by the air blow, temperature of the iron tip lowers. Accordingly, there arises a problem in that poor soldering is frequently performed just after the cleaning of the iron tip. Moreover, when the cleaning is carried out once in a plurality of times of the soldering, the soldering is performed in a state that new solder is supplied to the iron tip with old solder thereon until the next cleaning step is carried out. Accordingly, it is difficult to keep the solder of the iron tip at a constant amount. In view of this, there is a fear that uniform soldering is not performed.
By the way, when a circuit board is manufactured, dip soldering is performed in the following manner. Metal pins of electronic parts are inserted into holes formed in the circuit board on which wiring is printed. A face of the printed circuit board, from which the metal pins project, is dipped in a tub containing the solder melted by a heater. Then the metal pins are soldered together.
On the other hand, for circuit components protruding from the printed circuit board, a metal plate is provided in order to increase strength of its attachment by enlarging a soldering area. This metal plate is inserted into a slit formed in the printed circuit board after the printed circuit board was dip-soldered. The slit has a soldering land formed all around the slit. After insertion of the metal plate, the metal plate is soldered.
However, as shown in FIG. 5A, if a soldering land 81 is formed all around a slit 80, the slit 80 is sometimes closed by tension of solder 82 adhering to the soldering land 81 when the dip soldering is performed. The state that the slit 80 is closed with the solder is shown in FIG. 5B.
Moreover, as shown in FIG. 6A, when a soldering land 91 is formed half around the slit 80 in order to prevent from closing the slit 80, the slit 80 is not closed by the dip soldering. However, when a metal plate 93 is inserted into the slit 80 and soldered, the solder hardly goes round to the other side of the slit 80 where the soldering land does not exist. Thus, there arises a problem in that unsatisfactory soldering tends to be performed and sufficient strength is not obtained.